Malabsorption syndrome is usually defined as the complex of symptoms secondary to maldigestion and/or malabsorption, realizing when the extension of the disease exceeds the ability of intestine compensation. Several conditions have been recognized as being responsible for this syndrome. Up to now, different criteria have been used to order them, but a definitive classification is still not available because of the complexity of the absorption process, the involvement of different organs and structures, and the coexistence of different mechanisms in some diseases causing malabsorption. We propose a new classification of diseases causing malabsorption syndrome according to the responsible etiopathogenetic mechanisms: (a) alteration of digestive processes; (b) alteration of uptake and transport caused by damage or reduction of absorption surface, and (c) miscellaneous. A comment about the mechanisms responsible for malabsorption is given for all the cited diseases.